Investigation Of The Interface Between LPCVD-SiN_x Gate Dielectric And Iii-nitride For AlGaN/GaN MIS-HEMTs

Wide bandgap semiconductor Gallium nitride(GaN) is the current hot research in power devices. Compared to traditional silicon-based power devices, AlGaN/GaN heterostructure field effect transistors(HFET) have high breakdown voltage, low conduction losses and high switching frequency characteristics, which in power conversion and microwave communications fields show extremely outstanding application potential and advantages. Compared with the traditional Schottky-gate high electron mobility transistor(HEMT), AlGaN/GaN MIS-HEMT devices exhibit lower gate leakage current and larger gate voltage swing, more suitably applied to high voltage, high power and high reliability requirements of the work environment, and thus become the research focus of AlGaN/GaN HFET. Introduction of the gate dielectric in MIS-HEMT creates additional gate dielectric/nitride(III-Ntride) interface, in which the interface state traps and fixed charge will result in performance deterioration and reliability problems, such as the threshold hysteresis, current collapse and negative drift of threshold voltage, etc. Therefore, choosing a suitable gate dielectric materials and processing technology are the key to improve the interface performance and device reliability for AlGaN/GaN MIS-HEMT. In this paper, we adopt the silicon nitride(SiNx) grown by low pressure chemical vapor deposition(LPCVD) as the gate dielectric of AlGaN/GaN MIS-HEMT, and investgate the device performances and the interfacial properties. The main research contents are as follows:(1) Based on the wide bandgap semiconductor process chamber of Institute of Microelectronics, we adopted different deposition temperatures and annealing temperatures to deposite LPCVD-SiNx on n-type GaN epi wafer, and its bandgap value, the breakdown electric field and conduction band offset of GaN were respectively characterized. The LPCVD-SiNx dielectric grown at 650℃ and annealed at 830℃ showed the dielectric breakdown field of ~13MV/cm and conduction band offset of 2.75 eV. Furthermore, we adopted LPCVD-SiNx grown at 650℃ as the gate dielectric of AlGaN/GaN MIS-HEMTs, and completed the preparation of the associated device. The MIS-HEMTs demonstrated an off current ratio of ~1010, more than 12 V gate voltage swing, and breakdown voltage of 878 V corresponding to the drift region length LGD=20.0μm.(2) With the pulse transfer I-V method and multiple frequency and variable temperature C-V tests, LPCVD-SiNx/III-Ntride interface state distributions were investgated and characterized. In addition, using precise threshold voltage testing methods and band simulation, we extracted the equivalent fixed charge density of LPCVD-SiNx/III-Ntride interface. Finally, we achieved the interface states density between 1012~1013cm-2eV-1 from 0.3eV to 0.8eV wide energy level, and the equivalent interface fixed charge density of 2.6×1013cm-2.